Field
Aspects of the present disclosure relate generally to power gating circuits, and in particular, to an apparatus and method for supplying power to portion of an integrated circuit (IC) using weak-strong switch cells and strong-only switch cells, as well as method of designing power gating circuits.
Background
A power gating circuit is used for coupling a terminal voltage rail (TVDD) to an internal voltage rail (VDD) of an integrated circuit (IC). The terminal voltage rail (TVDD) receives an external supply voltage from a battery, regulator, or other type of source. The power gating circuit applies the external supply voltage to a portion (e.g., core or module) of the IC by electrically coupling the terminal voltage rail (TVDD) to the internal voltage rail (VDD).
A power gating circuit typically includes a set of switch cells for separately coupling the terminal voltage rail (TVDD) to the internal voltage rail (VDD). The set of switch cells typically include a subset of weak switch cells and a subset of strong switch cells. To limit an in-rush current, the weak switch cells are turned on first to allow the internal power rail (VDD) to partially charge up. Then, the strong switch cells are turned on to fully couple the terminal voltage rail (TVDD) to the internal voltage rail (VDD) such that the power gating circuit is able to supply the total demand for current (e.g., dynamic current) of the portion (e.g., core or module) of the IC.
Generally, there is a particular ratio of weak switch cells to strong switch cells (or total switch cells) that produces minimized in-rush current peaks. In the design phase of a power gating circuit, the ratio is estimated based on the design of the portion (e.g., core or module) of the IC. If the estimated ratio proves to be inaccurate, the power gating circuit needs to be redesigned by swapping weak switch cells for strong switch cells or vice-versa. Such swapping of cells requires re-routing of the connection of the power gating circuit to the IC portion, and performing timing analysis of the operation of the IC portion. Such interplay between redesigning the power gating circuit, re-routing, and timing analysis complicates the design of the IC, and often results in not achieving the optimal ratio of weak switch cells to strong switch cells (or total switch cells).